The present application claims priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application No. 2001-336510 filed on Nov. 1, 2001, the entire contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an oil pressure control system for automatic transmission of a saddle ride type four-wheel vehicle (buggy car) for running on rough terrain.
2. Description of Background Art
An automatic transmission of a general four-wheel vehicle, in most cases, does not have a mechanical neutrality maintaining mechanism, and interruption of transmission of power is effected by releasing the connection of a clutch. In the case where an oil hydraulic clutch is used, a primary oil pressure is disconnected forcibly by a manual valve. As for creep preventive control, for improvement of power consumption, a system is used in which the oil pressure of the clutch is interrupted based on a brake signal when a brake is applied, only for the first gear position, so that creep is generated when the control mechanism is in trouble. Where it becomes impossible to start the vehicle under a creep preventive condition, running at another position is possible.
In the case of a vehicle expected to be used on rough terrain, depending on the posture of the driver, it may be impossible to step on the brake, and thus it may be impossible to prevent creep with a creep preventive mechanism dependent on a brake signal. Therefore, a creep preventive mechanism which acts independently of a brake signal is required.
In addition, in the case where it becomes impossible to start the vehicle under a creep preventive condition, it is necessary to start from another position, so that a creep preventive mechanism only for the first clutch position is unsatisfactory.
The present invention has solved the above-mentioned problems.
A first aspect of the present invention is based on an oil pressure control system for automatic transmission for performing speed change by connection and disconnection of an oil hydraulic clutch provided alongside each speed change gear, wherein an oil pressure supply source for the oil hydraulic clutch is provided with a linear solenoid valve for supplying a working oil and interrupting the supply of the working oil, and the supply of the working oil to the clutch is interrupted when an internal combustion engine is in an idling condition and a vehicle is at stop.
According to this first aspect of the present invention, prevention of creep can be effected under all clutch conditions, and a neutral condition can be obtained by interrupting the supply of the working oil under a stand-by condition for starting (an idling stopped condition).
A second aspect of the present invention is based the oil pressure control system for automatic transmission, wherein the linear solenoid valve supplies the working oil when a power source is OFF, and interrupts the supply of the working oil when the power source is ON.
According to this second aspect of the present invention, since the power source is OFF during running, the problem of having running being impossible due to failure of the linear solenoid valve during running can be prevented.
A third aspect of the present invention is based on the oil pressure control system for automatic transmission, wherein the linear solenoid valve increases gradually the amount of the working oil supplied to the clutch, with increases in throttle opening and engine revolution frequency as parameters.
According to this third aspect of the present invention, abrupt starting due to abrupt connection of the clutch can be prevented.
A fourth aspect of the present invention is based on the oil pressure control system for automatic transmission, wherein the linear solenoid valve is provided with a communication passage for equalizing the pressure of the working oil supplied to the clutch and the oil pressure on the back side of the valve. The pressure of the working oil and the oil pressure on the back side of the valve are equalized when the working oil is supplied, and the pressure on the back side of the valve is released when the supply of the working oil is interrupted.
According to this fourth aspect of the present invention, when the output oil pressure is increased due to the balance of the thrust force of the solenoid and the pressure on the back side of the valve, the pressure on the back side of the valve is also simultaneously increased to close the valve, whereby the oil pressure is disconnected. With the oil pressure disconnected, the pressure on the back side of the valve is lowered, so that the valve is opened. These actions are repeated, whereby a constant oil pressure is outputted.
In addition to this, the thrust force of the solenoid is varied by a current value, whereby the output oil pressure can be varied linearly. By this, it is possible to gradually increase the pressure of the working oil that is supplied to the clutch.
A fifth aspect of the present invention is based on the oil pressure control system for automatic transmission, wherein a manual type emergency valve capable of forming an oil passage bypassing the linear solenoid valve is provided on the side of a discharge port of the linear solenoid valve.
According to this fifth aspect of the present invention, it becomes possible to start the vehicle even when a stop or failure has occurred under the condition where the linear solenoid valve is interrupting the supply of the working oil.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.